The spray-drying technique has seen wide application in the preparation of pharmaceutical powders, mostly for pulmonary drug delivery, with specific characteristics such as particle size, density and shape. It is a well-established method for producing solid powder by atomising suspensions or solutions into droplets followed by a drying process in flowing hot air.
Although most often considered as a dehydration process, spray-drying can also be used as an encapsulation method where active substances are entrapped in a polymeric matrix or shell. It is reported that several colloidal systems such as emulsions or liposomes were successfully spray dried with preservation of their structure using drying-aid agents, particularly sugars such as lactose, sorbitol and trehalose.
One of the merits of the spray-drying technique is that it is a cost effective and quick drying process applicable to a broad range of pharmaceutical products and leading to the production of a free flowing powder, characterized by very low water content, preventing therefore the degradation of the active. This is meaningful for the development of long-term stable carriers, mostly when these carriers are in the range of nano scale, designed specifically for the delivery of active compounds at the site of interest.
Recently, it has been shown that the spray drying technique can produce nano scale solid particles and solid lipid nanoparticles loaded with active agents to be used as delivery systems for pulmonary airways. It is worthwhile to note that in most cases where this technique was applied to produce solid nanoparticles, it was, in fact, a drying process of nanocapsules obtained by other techniques. Thereafter the suspension of the nanoparticles was subjected to spray drying. This resulted often in the production of particles with very broad size range from nano to micron size, despite the presence of disaccharides as drying excipients in the formulation.
Recently, it was reported the spray drying of a liquid colloidal system in the drug delivery field, where a single emulsion (water-in-oil emulsion) containing DNA encapsulated in poly(lactic-co-glycolic acid (PLGA), was successfully spray dried. Another report was made on spray drying of a double emulsion (oil-in-water-in-oil or O/W/O), in the presence of lactose, aiming to preserve orange oil and in both cases the particles produced were in the micron size range.
A need has been identified for spherical nanoparticles having a narrow size distribution range, typically from 180 to 250 nm. Ideally such particles should have a substantially smooth surface and be free flowing.